diff --git a/docs/source_docs/refs.bib b/docs/source_docs/refs.bib
index 899a6d64d461835eecfe9a802705999039bf0d66..98d10e53725a494db5040960ee7c901b52dfec5e 100644
--- a/docs/source_docs/refs.bib
+++ b/docs/source_docs/refs.bib
@@ -426,6 +426,16 @@ doi = {https://doi.org/10.1016/j.jcp.2022.111305},
   doi = {10.1063/1.864230},
 }
 
+@article{mehrabadi15,
+  title={Pseudo-turbulent gas-phase velocity fluctuations in homogeneous gas--solid flow: fixed particle assemblies and freely evolving suspensions},
+  author={Mehrabadi, M and Tenneti, S and Garg, R and Subramaniam, S},
+  journal={Journal of Fluid Mechanics},
+  volume={770},
+  pages={210--246},
+  year={2015},
+  publisher={Cambridge University Press}
+}
+
 @article{nijssen20,
   author = {Tim M.J. Nijssen and Hans A.M. Kuipers and Jan {van der Stel} and Allert T. Adema and Kay A. Buist},
   title = {Complete liquid-solid momentum coupling for unresolved CFD-DEM simulations},
@@ -528,7 +538,6 @@ doi = {https://doi.org/10.1016/j.jcp.2022.111305},
   publisher={Elsevier}
 }
 
-
 @article{suth1893,
   author = {William Sutherland},
   title = {LII. The viscosity of gases and molecular force },
diff --git a/docs/source_docs/user_guide/inputs/fluid_model.rst b/docs/source_docs/user_guide/inputs/fluid_model.rst
index 5d71749da0c36759dd2019ac6c790b3e679f3dec..b8ea64ff60113926cbb3d8fe1ef0e19ec99bad69 100644
--- a/docs/source_docs/user_guide/inputs/fluid_model.rst
+++ b/docs/source_docs/user_guide/inputs/fluid_model.rst
@@ -21,7 +21,9 @@ a single fluid; therefore, it is common to name the fluid ``fluid``. This is ill
 
 .. |Reid_4parm_Eq| replace:: :math:`\mu(T) = A\exp{\left( \frac{B}{T} + CT + DT^2 \right)}`
 
-.. |Sato_Eq| replace:: :math:`\mu^* = 1 + C d_s \rho \mu_{mol} \left|\boldsymbol{u} - \boldsymbol{u_s}\right|`
+.. |Sato_Eq| replace:: :math:`\mu_{pit} = C d_s \rho \left|\boldsymbol{u} - \boldsymbol{u_s}\right|`
+
+.. |eff_visc| replace:: :math:`\mu_{eff} = \mu_{mol} + \mu_{eddy} + \mu_{susp} + \mu_{pit}` 
 
 +--------------------------------------------+------------------------------------------------------------+--------+----------+
 |                                            | Description                                                |  Type  | Default  |
@@ -110,6 +112,10 @@ a single fluid; therefore, it is common to name the fluid ``fluid``. This is ill
 |                                            |                                                            |        |          |
 |                                            |      |Sato_Eq|                                             |        |          |
 |                                            |                                                            |        |          |
+|                                            | * ``Subramaniam`` :cite:p:`mehrabadi15`                    |        |          |
+|                                            |                                                            |        |          |
+|                                            |      :math:`\mu_{pit} = C_\mu k_f^2 / \epsilon_f`          |        |          |
+|                                            |                                                            |        |          |
 +--------------------------------------------+------------------------------------------------------------+--------+----------+
 | viscosity.suspension.Brinkman.constant     | Constant for exponent in Brinkman suspension expression.   | Real   | None     |
 |                                            |                                                            |        |          |
@@ -130,11 +136,14 @@ a single fluid; therefore, it is common to name the fluid ``fluid``. This is ill
 | viscosity.suspension.Sato.constant         | Constant for Sato suspension expression.                   | Real   | 0.65     |
 |                                            |                                                            |        |          |
 +--------------------------------------------+------------------------------------------------------------+--------+----------+
+| viscosity.suspension.Subramaniam.constant  | Constant for Subramaniam suspension expression.            | Real   | 0.09     |
+|                                            |                                                            |        |          |
++--------------------------------------------+------------------------------------------------------------+--------+----------+
 | viscosity.max_effective_factor             | Max limit of the effective viscosity as a factor of the    | Real   | 1.e6     |
 |                                            | molecular viscosity                                        |        |          |
 |                                            |                                                            |        |          |
 |                                            | :math:`\mu_{eff} < fac*\mu_{mol}`, where                   |        |          |
-|                                            | :math:`\mu_{eff} = \mu_{mol} + \mu_{eddy} + \mu_{susp}`    |        |          |
+|                                            | |eff_visc|                                                 |        |          |
 +--------------------------------------------+------------------------------------------------------------+--------+----------+
 | species                                    | Specify the species that constitute the fluid.             | String |  None    |
 |                                            |                                                            |        |          |